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Sometimes I wonder whether one could design PLC-style software by first expressing the system’s constraints and then writing the actual code and having either (preferably) formal verification that the code will not violate the constraints or (less preferably) enforced assertions that will send the machine into a safe state if the constraints do not hold.

The system I mentioned in my other post controlled some VFDs, and one would occasionally get stuck running at minimum speed forever instead of turning all the off when it should have. Fortunately the only harm done was a stupid waste of power and and nothing was physically damaged. If it had gotten stuck at maximum speed it might have been a different story.

by aliasxneo4 hours ago|

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A lot of PLC controllers can certainly be unforgiving. I mentioned overflowing a 16 bit float point because that's exactly what happened at a waste water treatment plant I was called out to and the resulting regulatory fiasco that ensued probably cost the company tens if not hundreds of thousands of dollars.

I'd love to see more formal methods come to the field. Part of me says I'll return one day, maybe if AI kicks me out of my software field, but I'd really want to come back at a position I could healthily influence towards safety and correctness.

by tedd4u3 hours ago|

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Seems like, here in the 21st century, one could reasonably have a model of the plant that tests could be executed against. Anything like that exist?

by aliasxneo3 hours ago|

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It can become really complex. As an example, try to predict resonant frequencies on an entire plant full of rotating equipment. It can be done, but it often requires very expensive equipment and skilled technicians capable of using it to profile a plant. And that's just one potential problem you can run into.

by Kim_Bruning3 hours ago|

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We're often talking about custom plants here, or plants made in very low volume. Making a simulator for that can be prohibitively expensive, since you can't amortize the cost. For particularly important/expensive plants it still sometimes gets done. Though note the simulator might not be able to capture all the nuances of the real world deployment, so it might not be sufficient.

Meanwhile having a separate copy of the plant is also not often viable, once the plants get to any kind of size.

edit: After having 'someone' fact check and remind me: there are quite a number of simulation tools available that can sometimes partially do the work.